Alloying



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ALLOYING Henry A. De Fries, Albany, N. Y., and Victor 0.

Homer-berg, Belmont, Mass assignors to Ludlum Steel Company, Watervliet, N. Y., a corporation of New Jersey Application May 22, 1928. Serial No. 279,131

4 Claims.

, Our invention relates to alloying. and particu larly to a new method of procedure whereby the production of alloys generally, both ferrous and non-ferrous, conforming to definite predeter- 5 mined analysis, is reduced to a pfactical mathematical certainty. It also relates to a method of procedure whereby the melting or freezing temperatures of the substances or alloys containing the elements to be incorporated together may be controlled to some extent whereby they may be brought suitably close to a common melting or freezing temperature.

vInthe introduction into steel or other metals of certain elements, such as aluminum, for example, there is no rational method of accurately predetermining the final content in the resulting product. Alloys closely approximating a definite specification may be made by cut and try methods but there isno way in which the production of an alloy having a definite composition can be controlled from the start and throughout the alloying operation.

In addition to providing a rational method of procedure whereby the production of an alloy conforming to a definite predetermined specification is made entirely practicable, our invention contemplates a method of controlling the melting or freezing temperatures of certain of the substances embodying the alloying elements whereby, in the case of steel for example, the melting or freezing of these substances may be fixed substantially at the freezing point of the steel itself.

We accomplish these objects by introducing the alloying elements into the steel or other metal, either as preformed alloys, approximating in composition true chemical compounds which are mainly intermetallic, as preformed compositions which are partially such compounds but which contain an excess-of one or more elements over and above the quantity which will combine with the other elements thereof to form a true compound, or by adding the alloying elements themselves in such proportions as will be adapted to form chemical compounds when intimately associated in molten condition.

Intermetallic compounds or chemical compounds which are mainly intermetallic have, of course, a definite composition and hence a definite freezing or melting point. Where two elements combine to form a definite compound an excess quantity of one element over and above that which will combine with the other to form such a compound either raises or lowers the freezing point. For example, iron and aluminum will combine to form the intermetallic compound FeAla having a freezing point of about 1180 degrees C. If the aluminum combined with a given amount of iron is in excess of that which will combine therewith as FeAla the freezing point is lowered, while if, on the other hand, the iron 60 is in excess of the FeAlz proportions, the freezing point is raised.

In the drawing, we have diagrammatically illustrated the effect on the freezing temperature of the possible variations in the composition of a magnesium-silicon alloy showing the existence of a chemical compound, MgzSl which is principally metallic and which has a freezing temperature of 1102 degrees C.

In addition to binary compounds such as FeAla, MgzSi, and AlNi, for example, it is quite possible to obtain ternary and more. complex compounds which are mainly metallic or intermetallic, such, for example a s'FeCrSiz. compound can be made by melting together high carbon chrome and ferro-silicori, containing 25% Fe, in such proportions as will give, in the final product, about equal parts of iron, chromium and silicon.

In the manufacture of an alloy steel conforming to the following specification, for example- Per cent Carbon 0. 40-0. 50 Chromium 8.0 -9.0 Silicon 3. 0 -3. 5 Iron Balance the intermetallic compound FeCrSiz may be used to advantage. Assuming a 10,000 pound heat and a desired silicon content of 3.5%, it would be necessary to add 350 pounds of silicon or say about 1000 pounds of FeCrSiz which is A; silicon. With the silicon would be added about 350 pounds or 3.5% chromium making necessary a further addition of about 500 pounds of chromium or 7 70 pounds total required chromium and the chromium in the silicide, and thereafter, add the silicide.

A steel containing aluminum, chromium and nickel and conforming to the following specifimaybe obtained by adding those elements in the form of an alloy or alloys conforming substantially in composition to intermetallic compounds. The aluminum and nickel might be added in the form of a compound, the chromium as ferrochrome or as an intermetallic compound of aluminum and chromium, or, a suitable ternary intermetallic compound of aluminum, chromium and nickel could be formed and incorporated in the steel bath as such.

If the above steel is to contain silicon, the most favorable intermetallic compounds to use would be FeCrSiz and FeAla. The quantity of FeCrSiz being calculated to give the desired silicon content, and the FeAla to give the aluminum content. The bath is made up from scrap, ferrochrome and nickel, and the intermetallic compounds added to the bath, the FeCrSiz being added first.

It is sometimes desirable to depart from a true intermetallic combination for the purpose of varying the melting or freezing temperature and getting it suitably close to that of the carbon steel. The intermetallic compound AlNi, for example, containing about 68% nickel freezes at 1645 degrees C. If the aluminum in an aluminum-nickel alloy is in excess of the amount required to form an intermediate compound, the freezing point is lowered, and a sufficient excess of aluminum, over and above that which will combine with the nickel to form a true compound, may be incorporated to lower the freezing temperature to the point desired.

In the drawing, which represents the equilibrium diagram of the magnesium-silicon system, it will be noted that the true intermetallic compound MgzSi freezes at 1102 degrees C. If a freezing temperature of 1050 degrees C. is more desirable in a given instance, the particular alloys of Mg and Si which will freeze at that temperature may be ascertained from the diagram. The points a and b where the horizontal temperature line of 1050 degrees intersects the curve are noted and projected to the base of the diagram-where the percentages of Mg and Si are read. In this case an alloy of Mg and Si containing either about 52% or magnesium will have the desired freezing temperature.

In the alloying of aluminum with steel, there are particular advantages in incorporating the aluminum in the form of the intermetallic compound FeAla. This compound is much heavier than aluminum and its melting point, 1180 degrees C. approaches more nearly the melting point of the steel itself. Hence. both are molten at more nearly the same temperature.

In the manufacture of chrome iron and stainless steels, containing aluminum and chromium, for example, we would first form one or more intermetallic compounds and then place the alloying elements together in solid solution. One such compound which can be formed contains approximately six parts of chromium and one part of aluminum. By adding the chromium and aluminum in this form, a solid solution of these elements is obtained in the steel, but in the form of what is believed to be an aluminum-chromium carbide.

By introducing the alloying elements into iron or steel in the form of alloys approximating in composition chemical compounds which are principally intermetallic we are enabled to definitely predetermine the alloy percentages which will ultimately be present in the iron or steel, thus making the production of alloys an operation which can be controlled from the start and throughout the alloying operation.

In addition to the above, the use of intermetallic compounds provides an improved procedure for incorporating easily oxidizable elements into iron or steel, and for introducing elements having relatively low melting points into metals having relatively high melting points, or vice versa.

While for illustrative purposes we have described the use of chemical compounds in connection with the alloying of iron and steel, it is to be understood that our method of procedure will be found of equal advantage in the production of non-ferrous alloys.

Where it is desired to produce an aluminumbronze conforming to the following specification, for example:

Aluminum 8 5-9 0 Iron 1.0-1.5

Copper Balance the intermetallic compound FeAla is particularly no suitable. Copper melts at about 1084 degrees C. but requires a superheat of about degrees C.

for alloying. FeAla melts at 1180 degrees C. or at practically the same temperature to which the copper must be heated. This being so, the compound FeAls aflords an excellent medium for introducing the required amount of iron into the copper. Part of the aluminum will be introduced with the iron and sufficient aluminum to make up the difference between the total required and the aluminum in the FeAla may be incorporated in the copper.

While the use of preformed chemical compounds of elements instead of the elements themselves in o be referred in all cases, because of the 12 definite c' .tainty with which the analyses of the final pr ducts can be predicted, it is possible in many instances to form the intermetallic compounds in the bath itself. This may be done by introducing the elements in such relative proportions as will adapt them to form chemical compounds when intimately associated in molten condition. This method of procedure, while possible, is fraught with uncertainty, and is therefore not as desirable as the use of preformed compounds.

What we claim isl. The method of alloying nickel and aluminum with steel which comprises incorporating them with the steel as a preformed composition con- 14; taining suflicient nickel to combine with part of the aluminum to form the intermetallic compound AlNi, and an excess -of aluminum suflicient to cause the temperature of freezing or separa- I tion of this compound from the liquid to approach the freezing temperature of the steel.

2. Those steps in the method of producing a ferrous alloy conforming to a definite specification nd containing a plurality of alloying elements which comprise combining different groups of said Per cent 105 elements in such proportions as to form separate compositions approximating chemical compounds, and thereafter combining said compounds in such proportions as to produce. in the alloy, the specified quantity of two of the elements in said comp n 3. Those steps in the method of producing a steel alloy conforming to a definite specification and containing nickel and aluminum with other elements which comprise, prealloying the nickel and aluminum in such proportions as to produce a composition approximating a chemical compound, and incorporating with the steel a sumcient quantity of the compound to produce, in the alloy, the specified quantity of one of the elements 01 the compound.

HENRY A. DE FRIES. VICTOR O. HOMIERBERG. 

